/*
 * Copyright (C) 2012 The Guava Authors
 *
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 * http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */

package com.google.common.collect;

import com.google.common.annotations.GwtCompatible;

import java.io.Serializable;
import java.util.List;
import javax.annotation.CheckForNull;

import org.checkerframework.checker.nullness.qual.Nullable;

/**
 * An ordering that treats all references as equals, even nulls.
 *
 * @author Emily Soldal
 */
@GwtCompatible(serializable = true)
@ElementTypesAreNonnullByDefault
final class AllEqualOrdering extends Ordering<@Nullable Object> implements Serializable
{
    static final AllEqualOrdering INSTANCE = new AllEqualOrdering();

    @Override
    public int compare(@CheckForNull Object left, @CheckForNull Object right)
    {
        return 0;
    }

    @Override
    public <E extends @Nullable Object> List<E> sortedCopy(Iterable<E> iterable)
    {
        return Lists.newArrayList(iterable);
    }

    @Override
    @SuppressWarnings("nullness") // unsafe: see supertype
    public <E extends @Nullable Object> ImmutableList<E> immutableSortedCopy(Iterable<E> iterable)
    {
        return ImmutableList.copyOf(iterable);
    }

    @SuppressWarnings("unchecked")
    @Override
    public <S extends @Nullable Object> Ordering<S> reverse()
    {
        return (Ordering<S>) this;
    }

    private Object readResolve()
    {
        return INSTANCE;
    }

    @Override
    public String toString()
    {
        return "Ordering.allEqual()";
    }

    private static final long serialVersionUID = 0;
}
